Rectilinear potentiometers



J. M. LOONEY, JR., ET AL April 11, 1961 RECTILINEAR POTENTIOMETERS 2Sheets-Sheet 1 Filed July l5, 1957 RECTILINEAR POTENTIOMETERS Filed Julyl5, 1957 2 Sheets-Sheet 2 FIG. 5 I FIGS ,276 /30 3/4 20a, /2/2 ,2402264`V9 564)(4 2792 2f?? SM2/302 f y f/IEZ/ f W. 204 /W 1 JOSEPH M.LOONEY, JR- ROBERT M. MARTIN ALTON FRASER United States Patent CRECTILINEAR POTENTIOMETERS Joseph M. Looney, Jr., Tarzana, and AltonFraser and Robert M. Martin, Van Nuys, Calif., assignors to TechnologyInstrument Corporation of Acton, a corporation of Massachusetts FiledJuly 15, 1957, Ser. No. 671,861

3 Claims. (Cl. SSS-183) This invention relates to variable resistors orpotentiometers and more particularly to new and improved rectilinearpotentiometers.

The primary object of this invention is to provide a new and improvedrecilinear potentiometer characterized by a unique coniiguration andmode of assembly that prevents relative motion between the resistancewinding and the contact-carrying member except for the normal desiredrectilinear movement of the contact-carrying member along the length ofthe resistance element, thereby resulting in improved noisecharacteristics under conditions of shock or vibration, as well asreduction in backlash or hysteresis.

Another object of this invention is to provide a rectilinearpotentiometer comprising a, resistance element, a carriage provided witha brush or contact member engaging the resistance element, and parallelguide ways supporting the carriage for rectilinear motion relative tothe resistance element, the carriage being so constructed and mounted onthe guide ways that it has freedom of movement onlyin the direction inwhich signal motion is introduced. y,

A further object of this invention is to provide a rectilinearpotentiometer adapted to be enclosed in a case which is so constructedthat the case is the last item to be attached, thereby permitting theunit to be tested before assembly is complete.

An additional object of this invention is to provide a rectilinearpotentiometer wherein the resistance element or elements can be shiftedlongitudinally, parallel to the wiper motion, for the purpose of phasingthe resistance elements toy any desired characteristic within thelimitations imposedby design. n f i v f Still another object is toprovide a potentiometer characterized by ease of assembly and a novelmode of securing the resistance element in place.

yOther objects and` many of the attendant advantages of the presentinvention will become readily apparent as reference is had to thefollowing detailed specification when considered together with theaccompanying drawings, wherein: D

Fig. lisa sectional view in side elevation ytaken along line 1-1 of Fig.3'of a preferred form of the present invention;`

y Fig.k2 is a sectional plan view of the same embodiment taken alongline.2,-2dof' 1 iig. 3;

Fig. 3`is an end view looking from left to right in Figl; n

Fig. 4is a viewin elevation of the opposite end of the samepdevice; d i

kFig. 5 ,is` a'scctional `view taken along line 5-5 of pighww :7,

Fig. 6 is a cross-sectional view of the brush carriage employed inltheembodiment ofFig. 1;

f Fig.V 7 is'fa sectional planview likefFig; 2 of a second form of thepresent invention; t l Fig. Adinan end view looking` fromright to'leftin Fig. 7i

Fig. 9 is a sectional view taken along 9-9 of Fig. 7; and

Fig. 10 is a cross-sectional view illustrating how the supports for theresistance element and the take-oli rod are flexed in order to beinserted in the potentiometer housing.

Referring now to Figs. l, 2 and 5, the rst form of the inventioncomprises two opposed support members 4 and 6, two opposed guide members8 and 10, and two circular end pieces 12 and 14. The support members,the guide members and the end pieces are all formed from aluminum.Support members 4 and 6 have been hard anodized to provide hardnon-conducting surfaces. It is to be understood that these members,particularly the support members 4 and 6, may be fabricated from othervarieties of insulating material, such as a phenolic resin or otherplastics. As best seen in Fig. 5, the supports 4 and 6 correspond incross-section to a segment on a chord of a circle and the guides 8 and10 correspond in cross-section to sectors of a circle. The opposite endsof each of the supports 4 and 6 are notched so as to fit into grooves 16and 18 cut into the inner surfaces oi the end pieces 12 and 14. Theopposite ends of guides 8 and 10 abut the inner surfaces of end pieces12 and 14. The end pieces 12 and 14 are secured to the guides 8 and 10by means of screws 20 and 22. The grooves 16 and 18 cut in the endpieces 12 and 14 are suiciently deep so as to permit the supports 4 and6 to be moved longitudinally a predetermined amount. However, the endpieces 12 and 14 are provided with tapped openings 24 and 26respectively in which are screwed set screws 28 and 30. The set screws28 and 30 prevent the supports 4 and 6 from moving. However, by turning'the screws 28 and 30 it is possible to adjust the positions of thesupports 4 and 6 relative to each other and also relative to the endpieces 12 and 14. In so far as already described, the assembly isself-supporting.

The supports 4 and 6 are provided with pairs of circular grooves 32 and34 respectively. Secured in one ofthe grooves 32 is a resistance elementA comprising a cylindrical core 38 on vwhich is wound a resistance wire40 formed of a suitable alloy A second resistance element B identical inconstruction is secured in one of the grooves 34. Secured in the othergrooves 32 and 34 are cylindrical take-oit bars C and D formed ofsilver.) or any other suitable conductor, as, for example, silverplatinum, palladium, gold, etc.' The resistance elements are secured tosupports 4 and 6 by any suitable means, as for example, a cement.

The electrical connections to the resistance elements and the take-offbars may be made in various ways. The preferred mode is describedhereafter.

Secured to the opposite yends of resistance elements A and B insurrounding engaging relation thereto are conductive terminals 46, 48,.y50 and 52. Secured to terminalsY 46 and 48 aretwo insulated leads 54 and56 which pass through suitable insulator bushings 58 provided inopenings in support member 4 and pass along a groove 60 cut in the outersurface of support member 4. The leads 54 and 56 run toward end piece12. The other support member 6 is provided with corresponding insulatorbushings 62 through which pass insulated leads 64 and 66 connected toterminals V50 and 52. Two additional wire leads and 72 are vconductivelysecured tothe take-off bars C and D at the ends nearest the end pieceV12.

The end piece 12 is provided with a cylindrical centrally located borein which is secured a terminal header 76 formed of glass or othersuitable material. imbedded in header 76 are three insulated terminalleads 78,` 80 ,and 82. Y The wire cores of these terminal leads extendthrough the header 76 into the open space defined by the acuosa supports4 and 6 and the guides S and 10. The leads 54, 56, 64 and 66 enter thesame space through openings 54- and 86 provided in supports 4 and 6.Leads 54 and 64 are conducti-vely connected to terminal lead 78. LeadsS6 and 66 are similarly secured to terminal lead 82. The leads 70 and 72running from the take-off rods C and D are connected to the terminallead 80.

As illustrated in Fig. 5, the guide ways and 10 are V-shaped and are sopositioned that their center lines reside in a common plane passingthrough the longitudinal `axis of the potentiometer.

The opposite end piece 14 also is provided with a centrally located borein which is secured a bushing 88. Bushing 8S is fabricated from bearingbronze or other suitable mater-ial and serves to supply a `hearingsupport for a shaft 90. Shaft 90 is formed of stainless steel or othersuitable material and is provided at its inner end with a brush carriageblock 92. Atiixed to shaft 92 is a retaining ring 94 which prevents theshaft from being pushed too far into the potentiometer body by limitingmotion to the point at which the ring contacts the bushing 88. The innerend of bushing 8S is counter-bored to receive a seal 96 formed of Telionor other suitable material such as nylon or rubber. The Teflon seal 96protects the inside of the potentiometer from external environmentalinfluences.

In the preferred form of this invention it is preferred that the brushcarriage block 92 be made of a suitable plactic such as Kel-F, a plasticbelonging to the general family of triiluoro-chloroethylene plastics.This material is preferred since it has excellent mechanicalcharacteristics in terms of tensile strength, low cold-dowcharacteristics, and high heat resistance characteristics, as well asbeing an insulator.

As seen in Figs. l, 2 and 5, the inner end of the shaft 90 is reduced indiameter so as to accommodate the brush block 92 and also to form ashoulder at 100 which engages one end of the block and prevents it frommoving up along the shaft toward end piece 14. The diameter of the endof the shaft on which the brush block is supported is sutciently smallto permit the shaft to rotate relative to the brush block. A bowedretaining ring 102 is secured to the inner end of the shaft and preventsthe block from moving away from the shoulder at 100 while stillpermitting relative rotation of the shaft.

As is quite clear from Figs. and 6, the brush block is H-shaped incross-section. The legs of the block are identified by numerals 106,108, 110, and 112.Y Secured to opposite sides of the brush block are twoconductive members 114 and 116 formed of beryllium copper or othersuitable material. These members are provided with pairs of tabs 11% and120 respectively which pass through small openings in the legs-of theblock and are secured thereto by a suitable cement. Secured betweenmembers 114 and 116 and the brush block are two pairs of precious metalbrushes or contacts 122 and 124. The brush members are conductivelysecured to members 114 and 116. Brushes 122 extend up away from thebrush block and lightly engage resistance element A and takeoff bar C.Brushes 124 contact resistance elementgB and take-off bar D. Thus whenshaft 90 is moved, the brushesl move along the resistance elements andthe take-off bars in the same direction. Y Y

Looking in particular to Figs. 5 and 6, it is apparent that the legs ofthe brush block, 106, 108, 110 and 112, yare relatively straightextensions of the brush block but have bevelled ends as at 130 forengaging the sloping sides of the V guides 8 and 10. Due to the lengthofthese legs and the angles of their bevelled end surfaces 130 (as well asthe geometrical configuration and positions of the guides), when theyare brought into engagement with the guides, they are stressed apart inthe direction shown by the arrows. For purposes of explanation, theamount bywhich the-legs are bent apart is slightly exaggerated in Fig.5. In practice the distortion is barely perceptible to the naked eye,being sufcient to prevent lateral shifting of the brush block. At thesame time, due to the tendency of the legs to return to unflexedposition, their bevelled ends contact the guides with just enoughfriction to prevent the brush block and the shaft to which it is aixedfrom sliding axially of their own weight when the potentiometer is heldon end. Thus only a slight force is required to move the shaft. Becauseof the preloading brought about by forcing the arms in the directionindicated by the arrows, only one degree of freedom of motion ispossible, that is, motion parallel to and along the guides. Motion ineither of the other two planes is restricted, since the configuration inwhich the ends of the brush carriage block are stressed eliminates allplay and consequently all lateral motion.

After the unit has been assembled and tested, a cylindrical housing 140is slipped over the assembly. This housing is also formed of anodizedaluminum or other suitable material. The housing has an inside diameterjust suicient to clear the outer surfaces of the support members `4 and6 and the guides 8 and 10 as well as the end piece 12. The end piece 14is provided with a peripheral ange 142 which acts as a stop for thehousing. The housing 140 is secured in place by screws 144 and 146`which are received in threaded openings provided in the guides 8 and10. An aluminum alloy mounting plate 148 is fastened to thepotentiometer housing by means of screws 1146.

In the second form of the invention illustrated in Figs. 7, 8 and 9, thebasic concept of a pre-loaded brush car riage running on parallel V waysis still inherent. However, in this form of the invention the parallel Vways are an integral part of the outside case or housing.

In this formV of the invention the outside case 200 is formed ofaluminum which has been anodized on its inside and outside surfaces. Asseen in Fig. 7, the housing consists of several portions of differentinside diameters and configurations. Commencing at the left of Fig. 7,the housing 200 is provided with an axial bore 204 in which is receiveda bearing 206. A set screw 208 screwed into a tapped radial opening inhousing 200 permits the position of the bearing to be adjusted. A shaft210 formed of stainless steel extends through the bearing 206. An 0ring212 makes a slip tit seal with the shaft 210. Positioned on the innerend of the shaft 210 is a brush carriage block 214 which is ofsubstantially the same cross-sectional configuration as the brushcarriage block or" the embodiment previously described. The end of theshaft is reduced in diameter to accommodate the brush block and also toform a shoulder 216 which abuts the brush block and prevents it frommoving back along the shaft. A retaining ring 218 prevents movement oftheV brush block in the opposite direction. As in the preferredembodiment, the shaft is rotatable relative to the brush block. Attachedto the brush block is a sleeve 220 which limits retraction of the shaftupon engagement with the bearing 206.` It is believed apparent that thestroke of the shaft in one direction can be adjusted by changing theposition of bearing 206. Attached to the brush block 214 by means ofberyllium copper conducting strips 222 and 224V similar to theconducting strips 114 and 116 of Fig. 6 are twoprecious metal brushes226 and 228, one on each sdeof the brush block. A copper shorting strip230 is connected to the strips 222 and 224.

Beyond the bore 204, housing 200 has an internal configuration asillustratedk in Fig. 9. This internal configuration is characterized bya pair of longitudinally-extendedsubstantially V-shaped ribs 2,32andr234 opposed to each other and a pair of curvedsurfaces 236 and 238havinga larger radius, of curvature than bore 204, thereare twoidentical e1ongated support members 244 and 246 fabricated from a Teflonor Kel-F extrusion. These support members have a main body portion 248defining a circular groove 250 and oppositely extending arms 252 and 254whose ends are bevelled to conform to the curvature of surfaces 236 and238 of the housing. The outer surface 256 of the body portion 248`of thetwo support members also is curved to coincide with the curved insidesurfaces 236 and 238 of the housing. The walls defining grooves 250extend through an arc in excess of 180. The configuration of the supportmembers is such as to provide pairs of grooves 260 and 262 between thebody portions and the arms 252and 254.

The function of members 244 and 246 is to clamp and support in positiona resistance element 264 and a takeott` rod 266 constructed like theresistance elements of the embodiment of Fig. 1.

When the support members are formed their arms 252 and 254 extendoutwardly too far to be received by the housing 200. In order to beplaced in the position shown in Figs. 7 and 9, it is necessary iirst tosqueeze the supports so as to liex their arms inwardly to the positionillustrated in broken lines in Fig. 10. When the supports are in theirunexed positions the grooves 250' are just large enough to receive theresistance element and the take-olf rod. When the arms of the supportsare bent toward each other, the body portion also bends so as toconstrict the groove 250' and clamp in place the resistance element andthe take-off rod.

The support for the resistance element is provided with two lateralopenings, one at each end of the resistance element, that run fromgroove 250 to grooves 260 and 262. The opening that leads to groove 260is shown in dotted lines at 270 in Fig. 9. The other opening is notshown but it is to be understood that it communicates with groove 262 atthe right hand end of the resistance element as seen in Fig. 7. Thepurpose of these lateral openings is to permit leads 272 and 274 whichrun along grooves 260 and 262 to be connected to the opposite ends ofthe resistance element. The connection with the resistance element ismade before the support 244 is inserted in the housing.

Immediately in front of the resistance element at the end nearest bore242, support 244 is provided with two openings which connect grooves 260and 262 with the interior of the housing. One of these openings isillustrated at 276 in Fig. 7. Insulated leads 272 and 274 pass throughthese openings into the interior of the housings. These leads are pulledthrough openings 276 and its counterpart before the support 274 isinserted in the housing.

The take-olf rod 266 is connected at one end to an insulated lead 280.This also is done before support 246 and rod 266 are inserted in thehousing.

Assuming that the two supports carrying the resistance element and thetake-olf rod have been flexed and inserted while llexed into thehousing, the karms 252 and 254 will tend to unex, but will be restrainedfrom doing so by the curved surfaces 236 and 238 of the housing incooperation with ribs 232and 234 which hold the supports against thecurvedsurfaces. In their restrained position the supports clamp theresistance element and the takeoff rod so as to prevent any relativemovement by the latter.

The supports engage the shoulder 240 and are prevented thereby frommoving` toward bore 204. Movement in the opposite direction is preventedby a circular header 282 which is securely positioned in bore 242 inabutting relation with the opposite end of the two supports. The header282 is formed of anodized aluminum which is provided with threeequiangularly positioned openings in which are secured glass tubes 284,each of which surroundsl and secures metal contact tubes 286 throughwhich extend leads 2,72, 274 and 280. Alternatively leads 272, 274 and288 may be conductively se cured to contact tubes 286 and/or tubes 286may be replaced by solid metal contact wires embedded in the glasssections 284. These tubes are in the 3, 6 and 10 oclock positions aboutthe center of the header. Due to the way Fig. 7 is taken, only two ofthe tubes 286 are shown. The header 282 also is provided with a tappedopening at its center in which is screwed a set screw 290. The latterfunctions as an adjustable stop for the shaft 210. A retaining tube 292holds the header in place. Potting 294 is positioned behind header 280and around tubes 286. The potting does not interfere with the set screw290.

Engaging the rear edge of the retaining tube 292 is an end piece 296which is held in place by a narrow retaining ring 298 positioned in agroove 300 in the housing. The inner surface of the end piece 296 isprovided with a tapered bore 302 which communicates with three deeplyangularly placed bores 304, 306 and 308. Fitting in the tapered bore isa frusto-conical plug 310 which is secured to the end piece 296 by meansof a screw 312. The diameter of the conical portion of the plug issmaller than the surrounding surface of the bore, leaving an annularspace therebetween to receive three insulated terminal leads 314 whichare conductively connected to the 4 three leads 272, 274 and 280 andpass through end bores 304, 306 and 308. It is to be noted that if leads272, 274 and 280 are conductively secured to the inner ends of the metalcontact tubes 286, terminal leads 314 may be conductively secured to theopposite ends of the same contact tubes. When the screw 312 istightened, the three leads 314 are compressed between the plug and theend piece, thereby holding them tixed. Thus any strain on the threeterminal leads cannot bertransmitted to the interior of thepotentiometer assembly, and particularly not to the resistance elementor to the take-off rod.

The advantages of the construction of Figs. 7, 8 and 9 are many. Amongthe more important advantages are the following:

(l) By utilizing a housing within which the V ways are an integralportion, it is possible to reduce the diameter of the potentiometer by aconsiderable amount,

(2) The element supports, which are fabricated from Teflon or Kel-F, notonly serve to support the resistance element and the take-off rod, butthey also serve as a clamp. This eliminates the need for securing thetakeoff rod and the resistance element to the supporting member by meansof a cement or some other material.

(3) The third advantage resides in the unique mode of clamping theterminal leads. VIt permits the internal leads of the potentiometer tobe brought out axially with the longitudinal axis of the potentiometercase and yet be easily clamped so as to prevent any strain from beingtransmitted to the interior of the potentiometer assembly.

It is to be understood that the brush carriage block in both embodimentsmay be made of metal, e.g., stainless steel. This would permit thepotentiometer to function at temperatures as high as 600-700 degrees F.In the event that the brush block is made of metal, it would benecessary to insert glass insulators into the block to which metal postscould be molded, to which the conductive members 114 or 222 could bewelded in order tcl irlizsulate them from the shaft and the brushcarriage b oc .f

It is to be understood that the resistance elements may be linear ornon-linear and may take the form of a fiat card secured to suitablesupports in a conventional manner. The resistance elements also may haveaddin tional taps. Where two resistance elements are employed,

they need not be connected in parallel, in which case additionalterminal leads will be provided. Similarly the cross-section of thehousing may be square or rectangular or have some other suitableconfiguration and the end pieces could be secured to the housing in asuitable manner other` than as illustrated and described.

The form of header may also be varied without departing from theprinciples of the invention. Moreover, as indicated previously,difierent materials may be used to fashion the various elements ofpotentiometers constructed according to the present invention.

Obviously other modifications and variations of the present inventionare possible in the light of the above teachings. Therefore, it is to beunderstood that the invention is not limited in its application to thedetails o construction and arrangement of parts specifically describedor illustrated, and that within the scope of the appended claims it maybe practiced otherwise than as specifically described or illustrated.

We claim:

l. In a potentiometer having a housing, a shaft extending longitudinallyof said housing, and means attached to said housing supporting saidshaft for rectilinear motion relative to said housing, the combinationcomprising a brush carriage attached to said shaft having an H-shapedcross-section, and comprising a body, a iirst pair of legs, and a secondpair of legs; the ends of said legs being beveled, and a pair of guideshaving sloping sides iisedly positioned within said housing andsupporting said carriage, said iirst and second pairs of legs eachhaving their ends in engagement with the sides of a guide and beingiiexed apart by said sides, whereby said carriage is movable back andforth along said guides and is held by said guides against lateralmovement within said housing.

2. A potentiometer comprising a tubular housing having opposite endwalls, each end wall having a groove in its inside surface, a resistanceelement consisting of a core and a resistance Wire wound about saidcore, an elongated resistance element support to which said resistanceelement is secured, said resistance element support located Within andextending longitudinally of said housing, said resistance support havingits opposite ends disposed in said grooves in said end walls, and setscrewsA projecting into said grooves and bearing against said oppositeends for selectively positioning said support and locking said supportagainst longitudinal movement out of a selected position.

3. In a potentiometer the combination comprising a cylindrical housing,a resistance element and an elongated support for said resistanceelement disposed within said housing, said resistance element comprisinga cylindrical core and a resistance wire Wound about said core, saidsupport comprising in cross-section a body portion and a pair ofoppositely extending arms, said support having a longitudinal groove insaid body portion, said groove having a size suiiicient to receive saidresistance element when said support is outside of said housing, thenormal distance between the ends of said arms when said support isoutside of said housing being too great for insertion of said support insaid housing without inward exing of said arms, said arms exed inward bysaid housing with said longitudinal groove constricted to clamp saidresistance element to said support.

References Cited in the le of this patent UNITED STATES PATENTS2,273,760 Nelson Feb. 17, 1942 2,339,721 Wilson Jan. 18, 1944 2,790,052Armstrong Apr. 23, 1957 2,813,183 Gearheart Nov. 12, 1957 2,850,607Bourns Sept. 2, 1958 2,857,497 Bourns Oct. 21, 1958 FOREIGN PATENTS397,935 Great Britain Sept. 7, 1933 741,391 Great Britain Nov. 30,A 1955

